In X-ray imaging, for example in computed tomography, angiography or radiography, use can be made of counting direct conversion X-ray detectors or integrating indirect conversion X-ray detectors.
X-rays or photons in indirect conversion X-ray detectors can be converted into light by a suitable converter material and via photodiodes into electrical pulses. Scintillators, for example GOS (Gd2O2S), CsI, YGO or LuTAG, are frequently used as converter material. In particular, scintillators are used in medical X-ray imaging in the energy range up to 1 MeV. Customarily, so-called indirect conversion X-ray detectors, so-called scintillator detectors, are used, in which X-rays or gamma rays are converted into electrical signals in two stages. In a first stage, the X-ray or gamma quanta are absorbed in a scintillator element and converted into optically visible light; this effect is called luminescence. In a second stage, the light excited by luminescence is then converted into an electrical signal by a first photodiode optically coupled to the scintillator element, read out by way of evaluation or read-out electronics and subsequently forwarded to a computing unit.
The X-rays or the photons in direct conversion X-ray detectors can be converted into electrical pulses by a suitable converter material. For example CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs or others can be used as converter material, in particular for use in a computed tomography system. The electrical pulses are evaluated by evaluation electronics, for example an integrated circuit (Application Specific Integrated Circuit, ASIC). In counting X-ray detectors, incident X-rays are measured by counting the electrical pulses which are triggered by the absorption of X-ray photons in the converter material. As a rule, the level of the electrical pulse is proportionate to the energy of the absorbed X-ray photon. By comparing the level of the electrical pulse with a threshold value, spectral information can be extracted.
A detector unit of a computed tomography system is known from the publication DE 10 2004 055 752 A1. The detector unit comprises a footprint which faces a support ring of a gantry of the computed tomography system in an assembly position, and a detector surface which is angled approximately vertically away from the footprint and faces an isocentric axis of the gantry in the assembly position and along which a number of detector elements for the detection of X-rays are positioned. The footprint has an air inlet which is fitted in such a way that a cooling air flow externally impinging on the footprint is routed to the inside of the detector surface. In the assembly position, the air inlet corresponds to an air duct in the support ring or routed between the winding carriage and the support ring.
An X-ray detector module comprising a sensor layer with a sensor surface in a stack formation is known from the publication DE 10 2013 226 666 A1, wherein a high voltage can be applied to the sensor surface for the detection of X-rays, wherein the sensor layer is thermally coupled to a latent heat storage system.
It is known from the publication DE 10 2014 201 741 A1 that in order to adjust the temperature of an X-ray detector of an X-ray machine comprising a plurality of adjacently arranged detector elements in which the X-ray detector and/or an X-ray source are moved relative to a measurement object during the acquisition of an X-ray image, a respective heat input measurement from the detector elements characteristic of the heat input into this detector element is recorded during the acquisition of the X-ray image, and the respective heat input measurement recorded for each detector element is taken into account when adjusting the temperature of at least one other detector element.
A radiation direct converter designed for the detection of X-rays and operated with a direct converter element having a temperature of at least 38° C. and at most 55° C. is known from the publication DE 10 2008 051 045 A1. The temperature can be adjusted via a Peltier element or an air flow.
In the operation of the medical device, the source of radiation and/or X-ray tube, in particular at high or full tube output, heats up greatly and must then be cooled down again as quickly as possible when treating patients to enable the recording of subsequent images. This is done by briefly increasing the fan speed of a cooling unit to the maximum value. This increases the pressure difference between the air intake side and the exhaust side and thus the amount of air which is transported through the so-called tube cooler. As the other users are connected to the tube cooler in parallel, however, these are now cooled in an above-average manner. As a rule, this does not disrupt the existing users as their work areas are designed for a particular, generally very generous temperature range and not for a temperature point. A direct conversion X-ray detector should display a constant operating temperature, however.